Typically the on-aircraft surface repair process includes filling a damaged surface region with an adhesive or other filler material so as to bring the surface of the damaged area flush with that of the adjacent undamaged surface areas. A repair patch is formed to substantially conform to the contour. The repair patch formed so as to overlap onto the adjacent undamaged surface area to obtain a metal-to metal (or composite-to-composite, as the case may be) bond region adequate to hold the repair patch in place. The repair patch is then adhesively bonded to the damaged area with a curing adhesive. The term adhesive is contemplated to include, but not limited to, epoxy resin, glue, cement and other bonding agents. Commonly, the adhesive requires heat to be applied to properly cure the adhesive or to accelerate the curing process.
In addition, trapped air is commonly encountered in the bondline between the structure and the repair patch and may take the form of small bubbles and volatiles where produce porosity in the bondline. During the curing process, however, these small bubbles may grow to become large bubbles or voids which significantly reduce the quality of the adhesive bond. It is known in the art that the application of uniform pressure to the repair patch during the curing process tends to squeeze out the trapped air in the bondline or otherwise mitigate the growth of the air bubbles into larger ones. Thus, the quality of adhesive bonding depends largely upon the application of substantially uniform pressure over the repair patch during the adhesive curing process.
A conventional method of applying pressure to the repair patch for on-aircraft repair involves using a flexible vacuum bag or cover. The vacuum bag is positioned over the repair patch and sealed around the perimeter. A vacuum or negative pressure source is applied to the vacuum bag so as to evacuate the vacuum bag, thereby collapsing the vacuum bag and forcing the vacuum bag against the repair patch. The amount of pressure applied to the repair patch is limited by the amount of vacuum pressure which may be achieved. For example, where there are holes or otherwise porous surfaces within the vacuum bagged area, such holes must be sealed prior to achieving adequate vacuum pressure. In addition, the sealing of the perimeter of the vacuum bag may present problems, especially where significant vacuum pressures are required to achieve a corresponding desired repair patch pressure.
Another method of applying pressure to an on-aircraft repair patch involves using tooling constructed specifically for a given repair. Obviously, such repair specific tooling is costly, labor intensive and inefficient.
Where the adhesive is a heat-curing adhesive, a heat source is additionally applied to the repair patch in conjunction with a pressure applicator. A conventional method for applying heat is through the use of a heating blanket.
Furthermore, aircraft surfaces in need of repair often are not located on smooth, flat, upward-facing areas. As such, repairs typically need to be effectuated surfaces which may be vertical or even downward facing. In addition, where the repair surface is located at an area of the aircraft which is contoured, the repair patch may be oriented significantly different from those surfaces immediately adjacent to the repair patch. For example, the convex curvature at the leading edge of the aircraft wings and the concave curvature where the wings intersect the aircraft fuselage present potential repair areas where the aircraft surface at the repair patch is significantly different from adjacent surface areas. Conventional pressure applicator devices may not be readily deployable at such contoured regions.
It is therefore evident that there exists a need in the art for a pressure applicator device for applying pressure to a repair patch during the curing process which facilitates on-aircraft repairs, applies substantially uniform pressure to the repair patch, accommodates the use of a heat source, such as a heating blanket, and is deployable adjacent a variable contoured aircraft surface.